Anomalous Exciton Condensation in Graphene Bilayers

In ordinary semiconductor bilayers, exciton condensates appear at total Landau-level filling factor nu(T) = 1. We predict that similar states will occur in Bernal stacked graphene bilayers at many nonzero integer filling factors. For nu(T) = -3, 1 we find that the superfluid density of the exciton condensate vanishes and that a finite-temperature fluctuation-induced first order isotropic-smectic phase transition occurs when the layer densities are not balanced. These anomalous properties of bilayer graphene exciton condensates are due to the degeneracy of Landau levels with n = 0 and n = 1 orbital character.